Since their discovery in 1991 (S. Iijima, Helical Microtubules of Graphite Carbon, Nature, 354 (1994) 56-58), CNTs have been investigated for many applications due to their unique and useful characteristics. A CNT can be considered as graphene sheets composed of fullerene structure of carbon atoms rolled up to form a tube shape. Multi-walled CNTs (MWCNTs) are typically on the order of a few micrometers long with a diameter up to one hundred nanometers. In case of single-walled CNTs (SWCNTs), diameters less than a few nanometers and lengths over a few hundred nanometers are common. CNTs are considered promising electro- and mechanical components due to high aspect ratio and a high mechanical strength with a ˜Tpa order of Young's modulus (D. Qian, G. J. Wagner, W. K. Liu, M. Yu, and R. S. Ruoff, Mechanics of Carbon Nanotubes, Appl. Mech. Rev. 55(6) (2002) 495-533). A CNT also shows fascinating electrical behavior such as semiconducting characteristics depending on chirality (P. L. McEuen, M. S. Fuhrer, and H. Park, “Single-Walled Carbon Nanotube Electronics”, IEEE Transactions on Nanotechnology, 1 (2002) 78-85). Also, the conductivity of some CNT is extremely sensitive to external environment including gas species [P. G. Collins, K. Bradley, M. Ishigami and A. Zettl, Extreme Oxygen Sensitivity of Electronic Properties of Carbon Nanotubes, Science 287 1801 (2000)]. The electrical, mechanical, chemical properties and characteristics of CNTs lend themselves to various end-use applications, as known in the art.
For instance, CNTs and arrays thereof assembled on micro/nano systems are useful in conjunction with a range of nanotechnologies and related device structures. Examples include ultra-high sensitive chemical sensors [Y. Ren and D. L. Price Appl. Phys. Lett. 79, 3684 (2001); P. G. Collins, K. Bradley, M. Ishigami and A. Zettl, Science 287, 1801 (2000); J. Kong, N. R. Franklin, C. Zhou, M. G. Chopline, S. Peng, K. Cho and H. Dai, Science 287, 622 (2000)], material characterization [M. F. Yu, O. Lourie, M. J. Dyer, K. Moloni, T. F. Kelly, and R. S. Ruoff, Science 287, 637 (2000)], and nanoelectronic devices. For such applications, input/output functions require accurate, reproducible placement and integration of highly ordered CNT nanoscale structures. FIG. 1 shows schematically a CNT configuration of the prior art for chemical sensing by electromechanical transduction.
Chemical vapor deposition (CVD) and chemical patterning methods have been used, but with limited success. CVD with methane gas is used to grow CNTs individually or as an array [Y. Zhang, A. Chang, J. Cao, Q. Wang, W. Kim, Y. Li, N. Morris, E. Yenlimez, J. Kong, and H. Dai, Appl. Phys. Lett. 79, 3155 (2001)]. High operating temperatures (˜900° C.) and extremely clean conditions are required to avoid the generation of amorphous carbon. With chemical patterning techniques, CNTs are deposited on a chemically functionalized region, but highly purified CNTs and complicated chemical treatment are necessary for successful deposition [Jie Liu, Michael J. Casavant, Michael Cox, D. A. Walters, P. Boul, Wei Lu, A. J. Rimberg, K. A. Smith, Daniel T. Colbert, Richard E. Smalley, Chemical Physics Letters 303 (1999) 125-129]. Process compatibility with either method and overall reliability remain critical issues.
The availability of highly-order CNT structures has remained a concern in the art. FIGS. 2(a) and (b) show deposition systems/methods of the prior art developed in response thereto. The electrostatic trapping method illustrated in FIG. 2(a) was designed originally to deposit a single Pd particle in an electrode gap [A. Bezryadin and C. Dekker, Appl. Phys. Lett. 71(9) (1997)]. A short circuit due to a reference resistance limits multiple depositions of Pd particles. However, the method was found unsuitable to the present concern as CNTs are not easily attracted by a direct current (dc) electric field and many unwanted particles in an applied CNT medium were instead deposited [K. Yamamoto, S. Akita, and Y. Nakayama, Appl. Phys. 31 (1998)]. FIG. 2(b) illustrates an alternating current (ac) electric field method of the prior art originally designed to deposit an Au rod in an electrode gap [P. A. Smith, C. D. Nordquist, T. N. Jackson, T. S. Mayer, B. R. Martin, J. Mbindyo and T. E. Mallouk, Appl. Phys. Lett. 77(9) (2000)]. The low resistance of the Au rod automatically limited multiple Au rod deposition. It was thought highly-oriented CNTs could be deposited between two such electrodes by applying an ac field, but multiple CNTs were observed as the depositions were not self-limiting [X. Q. Chen, T. Saito, H. Yamada, and K. Matsushige, Appl. Phys. Lett. 78(23) (2001)].